Rotary anode X-ray tube



Jan. 21, 1941. J, wALswEER no1-Am' Anous xfmvf TUBE- Filed Sept. 21, 1938 INVENTOR |71 Wilfh/ff/P ATTORNEY Patented Jan. 21, 1941 UNITED STATES Ronny ANoDE x-nar TUBE Y Johannes Waisweer, Glen Ridge, N. J., assigner to Westinghouse Electric Manufacturing Company, East Pittsburgh, Pa., a corporation of Delaware Application September 2l, 1938, Serial No. 230,911

4Claims.

The present invention relates to X-ray tubes and particularly to what are known in the art as rotating anode X-ray tubes. It has long been recognized that continued bombardment of the refractory metal target by the electron stream to cause the generation of X-rays localizes considerable heat on the surface of the target, which eventually melts the refractory metal surface, rendering the tube useless.

To overcome this disadvantage rotary anode X-ray tubes are now employed wherein the anode rotates during operation of the tube so that the electron beam is no longer confined to a restricted area of the target surface, but on the contrary impinges upon a larger area due to the rotation of the anode.

However, several disadvantages have been inherent in rotary anode X-ray tubes of the prior art, particularly the necessity for cooling the anode during operation of the tube by proper dissipation of the heat.

It is accordingly the primary object of the present invention to provide a rotating anode X-ray tube of compact construction and economical manufacture.

Another object of the present invention is the provision of a rotating anode X-ray tube wherein the stationary portion of the bearing of the anode forms a part of the envelope of the tube so that the heat generated during operation is readily dissipated to the atmosphere.

Another object of the present invention is the provision of a rotating anode X-ray tube wherein the discharge chamber is entirely metal enclosed, which renders the tube practically ray-proof without additional shielding.

Another object of the present invention is the provision of a rotating anode X-ray tube wherein the anode forms a closure cap for one end of the tube so that the heat generated during operation is readily dissipated to the atmosphere and wherein homogeneous electric iields are obtained within the tube with inherent shielding of the glass walls of the envelope from X-rays and secondary electrons, which reduces the possibility of envelope puncture by prevention of the accumulation of negative charges thereon.

A further object of the present invention is the provislo of a rotating anode X-ray tube wherein the anode is of a considerable mass of high heat conductivity metal which forms an end closure for the tube so that a substantial portion of the surface of the anode is exposed to the atmosphere to dissipate heat during operation of the tube and wherein the anode is provided with an opening (Cl. Z50-148) into which the concentrically disposed cathode projects, with the anode being provided with an angular surface having secured thereto a target of annular form adjacent the electron emitting surface of the cathode, resulting in an enclosed discharge chamber from which the X-rays are projected in the direction of the longitudinal axis of the tube.

Still further objects of the present invention wm become obvious to those skilled in the art 1 by reference to the accompanying drawing wherein:

Fig. 1 is a sectional view of a rotating anode X-ray tube constructed in accordance with the present invention;

Fig. 2 is a cross-sectional view taken on the line II--H of Fig. l, and

Fig, 3 is a sectional view of a stationary anode X-ray tube incorporating some of the features of the present invention.

Referring now to the drawing in detail, in Fig. l an evacuated vitreous envelope 5 is shown provided with a reentrant press 6 through which leading-in conductors 1 and 8 are sealed for supplying heating current as well as a negative potential to the cathode electrode. An inwardly projecting annular collar 9 is concentrically disposed with respect to the longitudinal axis of the tube and is formed of the same material as that of the envelope 5.

This annular collar 9 has sealed thereto an nnular metallic collar I0 having openings I 2 herein to enable exhaustion of the envelope through the exhaust tip I3, and the upper extremity of the annular metallic collar I0 has secured thereto a metallic member I4 of substantially cone shape and having an opening I5 extending therethrough. To facilitate assembly the upper portion of the metallic member I4 is provided with a detachable end I6 threadably connected thereto, which upper portion supports the thermionic emitting surface of the cathode I1 A parallel to the longitudinal axis of the tube.

One end of lthe thermionic cathode I1 is connected to the end portion I6 of metallic member I4 by means of a set screw I 8 and the opposite end of the thermionic cathode I1 is connected to the leading-in conductor 8 which extends upwardly through the opening I5 provided in the metallic member I 4 with the conductor 8 being insulated from the metallic member I4 and the upper end thereof I 6 by means of insulating bushings I9.

A shield 20 is provided to prevent scattered electrons from impinging upon the envelope in the vitreous material 5 of which the envelope is or the like.

formed.

Secured to this annular collar 22 is an anode, shown generally at 23, of considerable mass of high heat conductivity material, such as copper 'I'he anode 23 is shown as being of two parts, the upper portion thereof 24 forming a sealed end closure for the envelope and having a large portion of its exterior surface exposed to the atmosphere. A rotatable portion 26 of substantially annular form is secured to the upper portion by bearings 25 with a very small spacing therebetween so as to facilitate heat transfer between adjacent surfaces. The rotatable portion 26 is provided with an opening 21 into which the 25 thermionlc cathode projects, which thus forms an enclosed discharge chamber.

'I'he opening 21 is of substantially inverted frusto-conical configuration with the converging end flared outwardly to conform to the contour .o of the shield 20 and the angular surface 28 of the anode 23 is provided with an annular target 29 of refractory metal, such as tungsten or the like, which is disposed adjacent the electron emitting surface of the cathode l1 so that the electron beam emanating from the cathode impinges upon the annular target 29 and, due to the angle of the surface 28 carrying the target 29, the generated X-rays are projected from the itube in the form of a cone in the direction of its longitudinal axis.

In order to confine the cone of X-rays emanating from the tube to a restricted area, the sealed end closure cap portion of the anode 24 may be provided with a vitreous window 30 pervious to X-rays which is sealed to an annular member 32 having a coefficient of expansion approxirnating that of the vitreous window 30.

For the purpose of rotating the anode 23 upon the bearings 25, a stator winding 33 surrounds the envelope 5 exteriorly thereof and the surface of the anode 23 adjacent the stator Winding 33 is provided with laminations 34 of ferro-magnetic material. Also in order to shield the stator winding 33 the envelope may be provided with a suitable collar 35 of the same material as the envelope 5 sealed .thereto and substantially covering the stator winding. Likewise, in order to support the entire tube, a similar collar 36 may be provided.

Inasmuch as the cathode is disposed concentrically with the longitudinal axis of the tube and is surrounded by the annular shaped anode 23, an entirely metal enclosed discharge chamber, as before noted, is provided. Moreover, since the thermionic emitting surface of the cathode I1 is disposed parallel to the longitudinal axis of the tube and adjacent the refractory metal target carried by the angular surface on the inner periphery of the anode 23, the bombardment of the target by the electrons causes the generation of X-rays which are projected exteriorly of the envelope in the direction of the longitudinal axis of the tube and scattered X-rays or secondary emission are more or less precluded by the r'esulting metal enclosed discharge chamber.

By this arrangement very homogeneous electric fields are obtained within the tube whichto gether with .the metal enclosed discharge chamber, substantially eliminates the possibility of puncture due to secondary electrons which kotherwise would impinge upon the glass walls of the envelope, creating a negative charge on the surface thereof. Due to the considerable mass of which the anode is constructed and which has a substantial portion of its exterior surface exposed to the atmosphere, the heat generated during operation is readily dissipated to the surrounding atmosphere, thus increasing the emciency of operation of the tube.

In Fig. 3 an X-ray tube is shown which differs from that above described with reference to Fig. 1 in that it is of the stationary anode type. In this particular modification the envelope 5 has an annular metallic collar 42 sealed thereto of a material having substantially the same coeiilcient of expansion as that of the vitreous envelope material, which annular collar 42 supports an annular anode 43 of substantially the same construction as that above described relative to the anode 23 of Fig. 1.

However, in this modication the angular surface of the anode 43 is not of annular form, but is restricted to that portion immediately adjacent the electron emitting surface of the cathode I1. Like Fig. 1, the anode 43 in this modication forms -a substantial part of the envelope 5 and has a substantial portion of its exterior surface exposed so as to readily dissipate the heat generated during operation.

Again, as in Fig. 1, the anode 43 is provided with the window 30 sealed `to the annular member 32 having the same coeicient of expansion as that of the vitreous window. In al1 other respects the modification of Fig. 3 is substantially identical to that above noted with respect to Fig. 1. In addition, the envelope 5 of Fig. 3 may be surrounded by an outer envelope 44 of the same vitreous material as that of the envelope 5, which thus forms a chamber about the tube and such chamber may be filled with a material such as a liquid or gas which readily dissipates the heat generated during operation of the tube. It should be understood, however, that if a liquid cooling medium is utilized, the outer envelope would naturally be provided with a suitable expansion chamber or the like (not shown).

It thus becomes obvious to those skilled in the art that lan X-ray tube is herein provided in which the discharge chamber is entirely metal enclosed, and since the anode is of a considerable mass of high heat conductivity material having a substantial portion of its exterior surface exposed to the atmosphere, the heat generated during operation is readily dissipated.

Moreover, a compact X-ray tube is thus formed wherein the anode is of substantially annular form and by the provision of an annular target of refractory metal the anode may be rotated by generation of an electric eld, thus constantly renewing the target surface impinged by the electron beam and prolonging the useful life of the tube.

Although I have shown and described several embodiments of my present invention, I do not desire to be limited thereto as various other modications thereof may be made Without departing from the spirit and scopeof the appended claims.

I claim:

l. An X-ray tube comprising an evacuated envelope provided with a thermionic cathode and an anode surroundinig said cathode, said anode being of substantially annular form and provided with an annular target of 'refractory metal adjacent said thermionic cathode, a focusing cup for said cathode for confining electron bombardment of said target to a linear area to cause the X-rays generated at the target to be projected exteriorly of said tube in the direction of the longitudinal axis thereof and to form a foreshortened linear focal spot, and means disposed exteriorly of said envelope for rotating said anode about said cathode. v

2. An X-ray tube comprising an evacuated envelope provided with a thermionic cathode and an anode, said anode being ooncentrically disposed relative to said cathode and oi substantially cylindrical form, an annular target of refractory metal carried by said anode on the inner periphery thereof adjacent said cathode, a focusing cup for said cathode for confining electron bombardment of said target .to a linear area to cause the X-rays generated at the target to be projected exteriorly of said tube in the direction of the longitudinal axis thereof and to form a foreshortened linear focal spot, and means disposed exteriorly of said envelope for rotating said anode about said cathode.

3. An X-ray tube comprising an evacuated envelope provided with a thermionic cathode and an anode of substantially annular form and of considerable mass of high heat conductivity metal. means forming a closure member for one end o! said tube and having a large portion of its surface area exposed to the atmosphere for rotatably supporting said anode and for dissipating heat from said anode during operation of said tube, said anode having an opening therein into which said cathode projects and provided with an angular surface on its inner periphery adjacent said thermionic cathode, a target of refractory metal carried by the angularly disposed surface of said anode, and means disposed exteriorly of said envelope for rotating said anode about said cathode.

4. An X-ray tube comprising an evacuated envclope provided with a thermionic cathode and an anode of substantially annular form and of considerable mass of high heat conductivity metal, means forming an end closure for said tube and having a large portion of its surface area exposed to the atmosphere for rotatably supporting said anode and for dissipating heat from said anode during operation of said tube, an X-ray pervious window in said means for the egress of X-rays from said tube, said anode having an opening therein into which said cathode projects and provided with an angular surface on its inner periphery adjacent said thermionic cathode, a target of refractory metal carried by the angularly disposed surface of said anode, a focusing cup for said cathode for confining electron bombardment of said target to a linear area to cause the X-rays generated at the target to be projected exteriorly of said tube in the direction of the longitudinal axis thereof through said X-ray pervious window and to form a foreshortened linear focal spot, and means disposed exteriorly of said envelope for rotating said anode about said cathode.

, JOHANNES WALSWEER. 

